# Reynolds criterion

## Reynolds criterion

[′ren·əlz ‚krī‚tir·ē·ən]
(fluid mechanics)
The principle that the type of fluid motion, that is, laminar flow or turbulent flow, in geometrically similar flow systems depends only on the Reynolds number; for example, in a pipe, laminar flow exists at Reynolds numbers less than 2000, turbulent flow at numbers above about 3000.
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Definitive the parameters for calculating the Reynolds criterion: [T.sub.0] = [T.sub.f] = 0.5 x ([T.sub.f,in] + [T.sub.f,out])--the average temperature of the fluid in the: [R.sub.o] = [d.sub.in]--internal pipe diameter; [w.sub.0] = G/([rho] x f)--average by the pipe section velocity of the fluid movement.
Values of [[epsilon].sub.l] depending on the Reynolds criterion are presented in ,
where Nu is a dimensionless group called Nusselt criterion; C, n, m, p are coefficients; [Pr.sub.0], [Pr.sub.s] are Prandtl numbers correspondingly for cooling medium and cooling surface; [Gr.sub.0] is Grashof number for cooling medium; [Re.sub.0] is Reynolds criterion for cooling medium; [alpha] is value of heat exchange coefficient which is average for the exposed surface W/[m.sup.2][degrees]C; l is characteristic dimension, m; [lambda] is medium's coefficient of heat conductivity W/m[degrees]C.
Reynolds criterion characterizes speed of medium's movement in relation to solid body:
On one hand, water must flow with Re criterion as large as possible, so that the absorption of heat from the interior face of the tube should require small temperature drops and on the other hand, Reynolds criterion must be as small as possible so that the difference of pressure linked to water recirculation should be techno-economical acceptable.
The burning naval drop's experimental results, that were investigated in this paperwork, were made in the following standard conditions: ambient medium temperature, [T.sub.a] = 290 [+ or -] 1K ; temperature inside the burning room, [T.sub.ca0] = 973 [+ or -] 1K; fuel temperature, [T.sub.c] = 295 [+ or -] 1K ; pressure inside the burning room, [p.sub.ca0] = 103,325 [+ or -] 13kPa; burning room diameter, [D.sub.ca0] = 36 mm; fuel drop initial diameter, [D.sub.0] = 1,8 / 1,9 /2,0 mm ; air leaking regime surrounding fuel drop, estimated through Reynolds criterion, Re=80 /120 /140 ; drop's support and rapid insertion into the burning room by drop's propulsion charger, part of the ignition-burning simulator.

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